Unable to place 2 slabs in same block at y=255

Action to reproduce:

Place a stone brick slab at y=255
Then try to place a second stone brick slab on top of it, to create a full block

Expected behaviour:

2 slabs merge to form a single block

Actual behaviour:

On screen error "Height limit for building is 256 blocks"

Workaround:

Remove slab and replace with actual block